1. Field of the Invention
The present invention is directed to a medical device used during eye surgery. In particular, the present invention is directed towards a microkeratome for cutting a cornea of a patient's eye and creating a flap of corneal tissue.
2. Description of Related Art
Laser-assisted in-situ keratomileusis or LASIK surgery has become a fairly common procedure for correcting refractive errors in a patient's sight. Such LASIK surgery may eliminate or greatly reduce the need for the patient to use eyeglasses or contact lenses.
In LASIK surgery, a laser ablates a certain amount of corneal tissue to change the curvature of the cornea in order to reduce or eliminate the refractive errors inherently contained in the cornea. Before such laser ablation occurs in the LASIK procedure, a corneal flap is commonly formed with an instrument known as a microkeratome. A microkeratome is well known in the art, and generally includes a blade that is manually pushed or mechanically driven along a path across a suction ring, which holds the cornea in place during operation of the microkeratome. It is also common to oscillate the cutting blade in a direction transverse to a direction of the cutting path.
Unlike initial microkeratomes that removed a slice of corneal tissue from the eye, microkeratomes used in LASIK surgery create a flap with a corneal hinge. In other words, the microkeratome does not remove corneal tissue from the eye, but rather creates a flap which remains connected to the cornea of the patient at a hinge. Initially this hinge was created nasally or on the side of the eye by microkeratomes that traveled in a straight path across the suction ring. This allowed the main body and motor of the microkeratome to extend temporally from the patient. In this way the microkeratome avoided any interference with a patient's cheek, eyebrow, or nose during creation of the flap.
Microkeratomes then developed so that the hinge could be formed superiorly or at the top of the eye (known as a superior hinge). This was made possible by such microkeratomes as described in U.S. Pat. No. 5,624,456 to Hellenkamp, which description is incorporated in its entirety by reference. Hellenkamp avoided interference with a patient's anatomy by designing the microkeratome to be built vertically with the motor and cutting-head assembly directly above the cutting blade and pivoting across the suction ring. This allowed a superior hinge to be formed on the patient's eye, which many physicians believe is preferable to a nasal hinge because the superior hinge aligns with the blinking of the eye. In addition, such compact vertical design would even allow a nasal hinge to be formed.
While one embodiment of the Hellenkamp microkeratome has been a very successful commercial product known as the Bausch & Lomb Hansatome™, certain improvements to it and other pivoting microkeratomes are desired. For instance, the gear-track of the Hansatome may lead to jamming if the gear-track of the suction ring and the gear of the cutting-head assembly are not perfectly matched or if debris becomes lodged in the gear teeth. Therefore, it would be desirable to eliminate any gearing between the suction ring and the microkeratome cutting-head. The gearing also makes it difficult to mass-produce suction rings and cutting-heads which are interchangeable, which is highly desired for servicing and repairing the microkeratomes.
Other prior art pivoting microkeratomes, such as those available from Moria S.A. and known as CB microkeratomes or M2 microkeratomes have attempted to move the gear-track. Essentially, a crown gear has been formed on top of the pivot point in place of the gear-track of the Hansatome and a worm/worm gear interconnects the motor and the crown gear. Again, because of the gear interface between the suction ring and the cutting-head assembly, jamming is likely to occur. In fact, jamming may be more likely to occur on the CB unit because the torque required to pivot the microkeratome about a central pivot point is greater than the torque required for the outer gear-track of the Hansatome. The M2 attempts to overcome this jamming problem of the CB by substituting two motors to perform the function of one. That is, one motor for pivoting and a second separate motor for oscillating the cutting blade, thereby having more power available to overcome any gearing mismatch. This is in contrast to the Hansatome and the CB, which both use one motor for both the functions of translating the microkeratome across the suction ring and for oscillating the blade.
It would be desirable to provide a robust microkeratome design, which uses a compact and less expensive single motor design and still eliminates or greatly reduces the potential for jamming to occur. A single motor design is less expensive and potentially more reliable than a design utilizing two (2) motors, such as the M2.
Other prior art microkeratomes have avoided the potential for jamming during translation of the microkeratome head across the suction ring by simply eliminating a translation motor, and thereby, creating a manual microkeratome device which relies on the surgeon to push or pivot the microkeratome across the suction ring manually. However, it is believed that the consistency of depth of cut is sacrificed by the manual microkeratomes as are known in the prior art, as the thickness of the corneal flap is directly related to the speed of movement of the cutting-head across the suction ring. In addition, such prior art manual microkeratomes require a much more significant learning curve on the part of the surgeon than the use of an automated microkeratome.